.app {
  margin: 0 auto;
  display: flex;
  flex-direction: column;
  width: 600px;
  height: 600px;
  border: 1px solid #000;
}

.app .main {
  flex: 1;
  overflow-y: auto;
}

.app .footer {
  display: flex;
  justify-content: flex-end;
  align-items: center;
  height: 50px;
  border-top: 1px solid #000;
}

.app .main li {
  height: 50px;
  line-height: 50px;
}
